This section is intended to provide a background to the various embodiments of the invention that are described in this disclosure. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
FIG. 1 is an illustration of an example EUTRAN which is the air interface of the 3rd Generation Partnership Project's (3GPP) Long Term Evolution (LTE) of mobile communication networks. As is known among persons skilled in the art, the LTE radio access network uses a flat architecture with a single type of node, i.e. the evolved NodeB (eNB). The eNB is generally responsible for radio-related functions in one or several radio cells. As can be seen in FIG. 1, the eNB's are connected to the Evolved Packet Core (EPC) by means of the S1 interface. More particularly, the eNB's can be connected to a Serving Gateway (S-GW) by means of a S1 user-plane part, S1-u. Also, the eNB's can be connected to a Management Mobility Entity (MME) by means of a S1 control-plane part, S1-c. Furthermore, a Packet Data Network Gateway (PDN Gateway, P-GW) may connect the EPC to the Internet. Moreover, the X2 interface is the interface that connects the eNB's to each other. A more detailed description of the radio-interface architecture can be found in literature, such as in the reference book 4G LTE/LTE-Advanced for Mobile Broadband by Erik Dahlman, Stefan Parkvall and Johan Sköld, Academic Press, 2011, ISBN:978-0-12-385489-6, see e.g. chapter 8 “Radio-Interface Architecture”.
More mobile devices, smartphones, etc. are and will be equipped with multiple radio transceivers in order to access various networks. For example, a User Equipment (UE) may be equipped with LTE, WiFi, and Bluetooth transceivers, and Global Navigation Satellites Systems (GNSS) receivers. When the radio transceivers within the same UE, which are close to each other, operate on adjacent frequencies or sub-harmonic frequencies, transmissions associated with one radio transmitter may interfere with the receiver of another radio. This interference situation is referred to as an In-Device Coexistence (IDC) interference scenario, or IDC interference situation.
One approach to address this IDC interference problem, or IDC interference situation, is to minimize IDC interference between co-located radio transceivers by filtering. However, this may be technically challenging and expensive such that alternative solutions are needed. Another approach is to essentially move the interfering signal or signals either in frequency domain or in the time domain so that interference is reduced between the radios.
Currently, the 3GPP is standardizing signaling mechanisms for in-device coexistence (IDC) interference avoidance. The current status of the solution is described in a Change Request (CR) R2-124311 for the 3GPP Technical Specification TS 36.300. The R2-124311 was presented at a 3GPP meeting in Qingdao, China, Aug. 13-17, 2012. The contents of R2-124311 can be found in Appendix A (see also, ftp://ftp.3gpp.org/tsg_ran/WG2_RL2/TSGR2_79/Docs/R2-124311 zip)
In support of the IDC interference avoidance is the signaling between a UE and the network, e.g., a base station such as an eNB. A UE that supports IDC functionality indicates this capability to the network, and the network can then configure by dedicated signaling whether the UE is allowed to send an IDC indication. The UE may only send an IDC indication for E-UTRA uplink/downlink (UL/DL) carriers for which a Measurement Object (MO) is configured. When a UE experiences a level of IDC interference that cannot be solved by the UE itself and a network intervention is required, the UE sends an “IDC indication” via dedicated RRC (Radio Resource Control) signaling to report the IDC interference problem. The IDC indication is preferably triggered based on actual ongoing IDC interference on the serving and/or non-serving frequencies rather than on assumptions or predictions of potential interference. When notified of an IDC problem via IDC indication signaling from the UE, the eNB may apply, for example, a Frequency Division Multiplexing (FDM) solution or a Time Division Multiplexing (TDM) solution.
An example of an FDM solution is moving an LTE signal further away from the industrial, scientific and medical (ISM) band by performing inter-frequency handover within E-UTRAN to WCDMA or other similar technologies. An example of a TDM solution is to ensure that transmission of a radio signal does not coincide with reception of another radio signal during the same time slot or period. The LTE Discontinuous Reception (DRX) mechanism may be used to provide TDM patterns (i.e., periods during which the UE's LTE transceiver may be scheduled or not scheduled) to resolve IDC issues. A DRX-based TDM solution is preferably used in a predictable way, e.g., the eNB ensures a predictable pattern of unscheduled periods using a DRX type mechanism.
To assist the eNB in selecting an appropriate solution, IDC assistance information for both FDM and TDM solutions may be sent by the UE together with the IDC indication to the eNB. The IDC assistance information comprises, for example, a list of E-UTRA carriers suffering from ongoing interference, the direction of the interference, TDM patterns or parameters to enable appropriate DRX configuration for TDM solutions on the serving E-UTRA carrier, and/or an indication if interference is over. In case of an inter-eNB handover, the IDC assistance information is preferably transferred from the source eNB to the target eNB.
A prohibit mechanism, such as an IDC indication prohibit timer, may be used to restrict the time interval at which the UE sends an IDC indication in order to avoid unnecessary IDC indication signaling. For example, a prohibit timer can prohibit the UE from sending another IDC indication message soon after it previously sent an earlier IDC indication message. When the UE sends an IDC indication, the UE may start an IDC indication prohibit timer. The UE is generally not allowed to send a new IDC indication as long as prohibit timer is running. Alternatively, an IDC indication prohibit timer may be applicable to all new IDC indication messages. In this alternative, the UE may be further restricted to not send the same IDC indication content to the network as the UE sent earlier—irrespective of the status of the prohibit timer. Another alternative applies an IDC indication prohibit timer only to an IDC indication message whose content has changed from the previously sent IDC indication message.
A problem with these approaches is that an IDC indication cannot be sent by the UE even if it is actually needed, e.g. needed by the network. Although an IDC indication prohibit timer could be configured to a small value timeout to ameliorate this situation, a too short an IDC indication prohibit timer value can lead to a heavy signaling load consuming valuable radio resources as well as an increased computational load in network nodes.